This invention relates to an anaerobically curable sealing composition essentially comprising an acrylic ester or a methacrylic ester (hereinafter stated as a (meth)acrylic ester), having excellent anaerobic characteristics and outstanding storage stability.
An anaerobically curable sealing composition essentially comprising a (meth)acrylic ester is characterized in that the composition will be kept stable in liquid state as long as it remains in contact with air or oxygen, while rapidly curing under the exclusion of air or oxygen. Thus, the composition is widely used in all fields of industries as adhesives, loosening prevention materials for bolts and nuts, and leak-preventing materials.
As the above-mentioned anaerobically curable sealing compositions comprising a (meth)acrylic ester, compositions having a (meth)acrylic ester as a polymeric monomer and an organic peroxide as its main ingredients have been known in the art, such as in the Japanese Pat. Publication Nos. 35-2393, 38-3595, the U.S. Pat. No. 3,435,012 and also in the Japanese Pat. Publication No. 45-17080. In these compositions are used such organic peroxides as cumen hydroperoxide, di-alkyl peroxide, etc. These organic hydroperoxides are comparatively appropriate in that they provide to the obtained compositions anaerobic characteristics, but the cure accelerating agents and other components contained in the compositions containing a hydroperoxide have a disadvantage that they give rise to a decrease in adhesive force after a long storage and are deficient in storage stability.
The inventors of this invention have successfully found methods to obtain anaerobically curable compounds, which have greater adhesive force, compared with conventional anaerobically curable sealing compositions having a hydroperoxide or a di-alkyl peroxide as a polymerization initiator, and are excellent in storage stability, by way of using 3,6,6,9,9-penta-methyl-3-n-butyl-1,2,4,5-tetra-oxacyclonine (hereinafter called Composition (1)) among the peroxiketanol group, having the structural formula of ##STR1## as a polymerization initiator of the afore-mentioned anaerobically curable sealing compositions comprising of a (meth)acrylic ester.